Abstract

Noise characteristics of second-harmonic generation (SHG) in
periodically poled lithium niobate (PPLN) using the quasiphase
matching (QPM) technique are analyzed experimentally. In the
experiment, a0.78 𝜇m second-harmonic (SH) wave was generated when
a 1.56 𝜇m fundamental wave passed through a PPLN crystal (bulk or
waveguide). The time-domain and frequency-domain noise
characteristics of the fundamental and SH waves were analyzed. By
using the pump-probe method, the noise characteristics of SHG were
further analyzed when a visible light (532 nm) and an infrared
light (1090 nm) copropagated with the fundamental light,
respectively. The noise characterizations were also investigated
at different temperatures. It is found that for the bulk and
waveguide PPLN crystals, the SH wave has a higher relative noise
level than the corresponding fundamental wave. For the same
fundamental wave, the SH wave has lower noise in a bulk crystal
than in a waveguide, and in MgO-doped PPLN than in undoped PPLN.
The 532 nm irradiation can lead to higher noise in PPLN than the
1090 nm irradiation. In addition, increasing temperature of device
can alleviate the problem of noise in conjunction with the
photorefractive effect incurred by the irradiation light. This is
more significant in undoped PPLN than in MgO-doped one.